1. Field of the Invention
This invention relates to polyester amides and to methods of preparation thereof and is more particularly concerned with polyester amides derived from a carboxylic acid terminated polyester prepolymer and methylenebis(phenyl isocyanate) and or toluene diisocyanate, and with processes for the preparation of said polyester amides.
2. Description of the Prior Art
The term polyester-amide is commonly employed to cover a diverse group of polymers which are characterized by the presence of recurring amide and ester linkages in the molecule thereof. The members of this group have been investigated hitherto largely in regard to formation of fibers and films. To the best of the present inventors' knowledge, no polyester-amides have been described which are capable of being processed by injection molding techniques to give molded articles having sufficiently satisfactory physical properties (including resistance to degradation at high temperatures) to enable them to be used as seals, gaskets, bushings, and in like applications for thermoplastic elastomeric polymers.
A number of instances have been reported in which segmented polyester-amides have been prepared in order to provide polymers, useful primarily for fiber formation, in which the requisite balance has been sought between the physical properties contributed by the "soft" polyol segments and the "hard" polyamide segments. Illustratively, British Pat. No. 1,170,300 describes the preparation of segmented polyester amides by reaction of the acid chlorides of carboxy-terminated polyesters with a series of relatively complex diamines which contain a plurality of amide linkages. U.S. Pat. No. 3,044,987 describes the preparation of fiber-forming segmented polyester amides by the reaction of the acid halide of a carboxy-terminated polyester with a simple diamine and, optionally, a difunctional acid halide. The resulting polymers contain "soft" segments derived from the polyol residue and "hard" segments derived from the diamine. It is apparent from the specific examples given in the reference that polymers having relatively low melt temperatures (of the order of 250.degree. C.) or less are obtained provided no aromatic moieties are introduced into the soft or hard segments of the polymers. However, introduction of an aromatic moiety, specifically the terephthalic acid residue, into either the soft or hard segments gives polymers having melt temperatures in excess of 300.degree. C. which renders them incapable of being processed by injection-molding techniques.
In order to produce polyester-amides which will have sufficient structural strength properties to produce useful articles by injection-molding techniques it is highly desirable to be able to introduce aromatic residues into the soft and or hard segments. But this has to be achieved without raising the melt temperature of the polymer above about 280.degree.-300.degree. C. otherwise the polymer is no longer moldable by injection molding techniques.
We have now found that these various objectives can be attained by employing very carefully selected combinations of reactants and reaction conditions in the preparation of the polyester-amides as will be described in detail hereinbelow.